feat(joinir): Phase 224-E - DigitPos condition normalization

Add DigitPosConditionNormalizer to transform integer comparison to boolean:
- `digit_pos < 0` → `!is_digit_pos`

This eliminates the type error caused by comparing Bool carrier with Integer:
- Before: Bool(is_digit_pos) < Integer(0) → Type error
- After: !is_digit_pos → Boolean expression, no type mismatch

Implementation:
- New Box: digitpos_condition_normalizer.rs (173 lines)
- Pattern2 integration: normalize after promotion success
- 5 unit tests (all pass)
- E2E test passes (type error eliminated)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs

@@ -240,7 +240,7 @@ impl MirBuilder {
 
         // Wrap condition in UnaryOp Not if break is in else clause
         use crate::ast::UnaryOperator;
-        let break_condition_node = if break_in_else {
+        let mut break_condition_node = if break_in_else {
             // Extract span from the raw condition node (use unknown as default)
             let span = crate::ast::Span::unknown();
 
@@ -328,6 +328,21 @@ impl MirBuilder {
                                 ));
                             }
                         }
+
+                        // Phase 224-E: Normalize digit_pos condition before lowering
+                        // Transform: digit_pos < 0 → !is_digit_pos
+                        use crate::mir::join_ir::lowering::digitpos_condition_normalizer::DigitPosConditionNormalizer;
+                        break_condition_node = DigitPosConditionNormalizer::normalize(
+                            &break_condition_node,
+                            &promoted_var,
+                            &carrier_name,
+                        );
+
+                        eprintln!(
+                            "[pattern2/phase224e] Normalized break condition for promoted variable '{}' → carrier '{}'",
+                            promoted_var, carrier_name
+                        );
+
                         // Carrier promoted and merged, proceed with normal lowering
                     }
                     ConditionPromotionResult::CannotPromote { reason, vars } => {